Dehydration in children

Causes and risk

Diarrheal illness is where oral rehydration is called for, and most such illnesses are viral. Fluid is also lost through drugs and through metabolic states:

• Hypertonic osmotic laxatives, such as milk of magnesia, magnesium citrate and sodium phosphate, draw water into the bowel, so they carry a risk of electrolyte abnormalities and of dehydration and are used with caution in older adults and in renal impairment.
• In diabetic ketoacidosis dehydration is one of the signs.
• In the hyperosmolar hyperglycemic state, severe hyperglycemia raises serum osmolality with osmotic diuresis, and the dehydration is profound. The elderly are more susceptible to it than younger people.

Dehydration is itself a cause of other problems: it is listed among the common triggers of vasovagal syncope, with pain, emotional stress and prolonged standing, and among the causes of orthostatic hypotension.

Several diabetes drugs are stopped when dehydration is a risk, and the reason differs by drug. Some oral hypoglycaemics are stopped temporarily during an acute illness and restarted once the person is feeling better and eating and drinking for 24-48 hours. Metformin is stopped if there is a risk of dehydration, to reduce the risk of lactic acidosis. SGLT-2 inhibitors are stopped if the patient is acutely unwell or at risk of dehydration, with ketones checked, because of the risk of euglycaemic DKA. GLP-1 receptor agonists are stopped if there is a risk of dehydration, to reduce the risk of AKI. Sulfonylureas may increase the risk of hypoglycaemia. Insulin is not stopped. What is lost is not the same in every diarrhea. In secretory diarrhea such as cholera the sodium and potassium concentration in the diarrheal fluid is similar to the concentration in plasma, while in most bacterial and viral enteritides it is less than in plasma, so an identical volume of diarrheal fluid lost has a different effect on electrolyte concentration and volume status. The children at greatest risk are those under 1 year and particularly under 6 months, infants who were of low birth weight, children who have passed more than five diarrheal stools in the previous 24 hours, and children who have vomited more than twice in the previous 24 hours.